First-degree heart block affects the electrical signal that makes the heart beat, causing a slower or abnormal rhythm. There are three degrees of heart block — first-degree heart block does not usually have symptoms or require treatment.

Doctors call heart block atrioventricular (AV) block. It is a type of arrhythmia, or irregular heartbeat.

People may experience AV block that is first, second, or third degree. First-degree heart block is the least serious.

This article discusses what first-degree heart block is. It will also cover the causes, symptoms, treatment options, diagnosis methods, and prevention.

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Heart block is a type of arrhythmia, which means irregular or abnormal heartbeat. When someone has heart block, it means their heart can beat slowly or miss beats.

The heart pumps blood around the body and has four chambers. The atria are at the top, and the ventricles are at the bottom.

Typically, electrical signals travel from the atria to the ventricles through a group of cells in between them, called the AV node. It is what makes the heart beat and push blood through the chambers.

When someone has heart block, the electrical signals cannot get through the AV node. This stops the heart from pumping blood as well as it should.

There are three types of heart block. First-degree heart block is the least serious. John Hopkins states that the electrical signals slow down as they travel from the atria to the ventricles.

Learn more about how the heart works.

According to the United Kingdom’s National Health Service (NHS), first-degree heart block is the mildest form of the condition. People do not usually notice any symptoms and may not require treatment.

However, it can sometimes progress to second- or third-degree heart block.

In some cases, a person can be born with heart block. This is called congenital heart block.

However, it typically develops as a person ages. This happens when the AV node develops fibrosis, which is the thickening or scarring of the tissue.

A 2022 article notes that 1–1.5% of people under 60 years experience heart block, and around 6% of people over 60 have the condition.

It is also more common in males and athletes.

Some risk factors include:

Other medical conditions that can cause first-degree heart block include:

People with first-degree heart block will not usually have any symptoms. Most people are unaware they have the condition until they go for a routine electrocardiogram (ECG).

The American Heart Association (AHA) notes that some people may experience lightheadedness or dizziness.

Second- and third-degree heart block

According to the AHA, second-degree heart block occurs when electrical signals do not reach the ventricles.

There are two types of second-degree heart block. The first is called Mobitz type 1. It is less serious and is unlikely to cause symptoms. However, people may feel faint or lightheaded.

The second type of second-degree heart block — Mobitz 2 — is more serious and can lead to:

Third-degree heart block stops the electrical signal altogether. This makes the heartbeat irregular and unreliable, which can lead to serious health problems. Symptoms can include:

  • fainting
  • chest pain
  • shortness of breath
  • extreme tiredness

The symptoms of third-degree heart block can be life threatening and people should seek emergency medical help.

In the majority of cases, people with first-degree heart block do not need treatment. If people are not experiencing symptoms, doctors are likely to monitor a person’s heart to determine if the condition worsens.

For people who experience heart block symptoms or those who have heart block as a result of a heart attack, doctors may recommend a pacemaker. This is a small device that a cardiac surgeon places under the skin in the chest. It sends electrical signals to the heart, helping to control the beat.

To diagnose first-degree heart block, doctors will usually:

  • ask the person about their medical history
  • carry out a physical exam, including listening to the heart

They will also do an ECG test. This records the heart rate, its rhythm, and the timing of the heart’s electrical signals.

First-degree heart block is not usually serious, and people can lead a usual life, providing the condition does not progress. However, people will require regular monitoring.

If the heart block worsens, complications can include:

  • injury as a result of fainting
  • low blood pressure
  • heart attack
  • damage to other internal organs

For people with some congenital heart issues, the causes of heart block are present when they are born. As such, a person cannot always prevent it. However, if a pregnant person has an autoimmune condition, certain treatments can reduce the chance of congenital heart block.

In some cases, there are ways to prevent the causes of heart block. People should focus on maintaining a healthy lifestyle, which includes:

  • exercising
  • following a healthy, balanced diet
  • avoiding smoking

If people are taking medications, they should discuss the potential side effects and risks with a doctor.

First-degree heart block does not usually interfere with a person’s life. However, people should try to maintain a heart-healthy lifestyle, including exercising and following a balanced diet.

Learn more about the cardiac diet.

Doctors may recommend that people with pacemakers avoid some types of exercise. These tend to be sports that involve body contact.

Anyone who experiences the symptoms of heart block should speak with a doctor as soon as possible.

Most people with first-degree heart block will not experience symptoms. That is why it is important to have regular health checks.

The AHA recommends people undergo some routine cardiovascular screening tests from the age of 20.

Heart block is a type of arrhythmia. It means electrical signals in the heart are not working as they should, slowing the heartbeat.

First-degree heart block is the least serious form of the condition. Most people will experience no symptoms and need no treatment.

However, heart block can progress, or worsen. If this happens, doctors may recommend a pacemaker.

People should adopt a heart-healthy diet and lifestyle to help prevent heart block from developing.